Why coating is crutial for Al Masts?

Discussion in 'Materials' started by metin_mehel, Jan 3, 2014.

  1. metin_mehel
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    metin_mehel mech.eng.

    Hello,

    I heard that the Aluminium masts have Al2O3 coating. But Aluminium
    naturally has this coating without treatment.
    Why it is needed this additional or thicker Al2O3 coating?
    Thanks
    Metin :confused:
     
  2. gonzo
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    gonzo Senior Member

    It is a harder and more corrosion resistant finish. Also, it gives the possibility of having a variety of colors.
     
  3. Richard Woods
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    Richard Woods Woods Designs

    A coating also adds protection for the aluminium when fitting stainless steel tangs etc. Even if using zinc chromate paste (for example) corrosion can occur over time.

    These days many people spray-paint bare aluminium as anodising is often expensive and its difficult to find somewhere that can do a long mast

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  4. messabout
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    messabout Senior Member

    An anodized surface is dielectric. That is to say that it does not conduct elecricity well or at all. Thus it is less likely to be attacked by galvanic corrosion, an electrolytic process. A stainless tang or other disimilar metal attached to bare aluminum will eventually develope some corrossion which attacks the aluminum more than the stainless. Anodizing delays the process quite well. Most good quality paints will perform the same duty as long as the film between the parts is intact. Beware of aluminum infused paints in these circumstances, some of the aluminum paints do conduct electricity though not very well.

    Want to check the mast or boom extrusion to tell whether it is anodized? Get out your volt-ohm meter. Anodized parts will show very large resistances on the ohm scale.
     
  5. rainmaking
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    rainmaking Junior Member

    There are treatments that don't affect conductivity that help corrosion resistance: iridite, alodine, chromate conversion are a few. Fastening should either be with a durable zinc coated fastener -look for zinc flake- or it should be insulated if it is a structural connection. Do not use bare stainless even if the aluminum is anodized.
     
  6. FAST FRED
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    FAST FRED Senior Member

    I have seen more damage by corrosion UNDER the coating than from a bare aluminum mast.

    If you want the easiest to live with,, bare aluminum covered with the oil (it dries) that is used by concrete form folks seems to make the stick last longest.

    I have seen folks chose the other option , spend big time polishing the stick, to cut down on the surface area.
     
  7. metin_mehel
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    metin_mehel mech.eng.

    Thank you for the answers...
    I have Al6061 tube. I will will use it as the mast.
    I wonder what happens?
    Thanks...
     
  8. rainmaking
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    rainmaking Junior Member

    You can buy small amounts of the chemicals to Alodine or iridite your tube. They can be painted on. This will drastically cut down on the maintenance time if using the vessel in salt water.
     
  9. metin_mehel
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    metin_mehel mech.eng.

    I think I can not find a supplier of this material here at my country.
    Thanks
     
  10. metin_mehel
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    metin_mehel mech.eng.

    I found some suppliers thanks...
    Is it better than Al2O3?
     
  11. rainmaking
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    rainmaking Junior Member

    Depends on what your requirements are. It does not have the same corrosion resistance, but in your application you can probably maintain it better than anodize (Al2O3).
     
  12. metin_mehel
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    metin_mehel mech.eng.

    Do you realy think Alodine kind coatings are better then Al2O3? Because it is very common and almost every mast manufacturer use Al2O3.
     
  13. metin_mehel
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    metin_mehel mech.eng.

    I did not understand the bare stainless steel and Al made a junction and the corrosion relationship.
    Thanks
     
  14. metin_mehel
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    metin_mehel mech.eng.

    Hello,
    Is this page good for understanding what is going on?
    http://www.aluminiumdesign.net/design-support/aluminiums-corrosion-resistance/
    Thanks
     

  15. metin_mehel
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    metin_mehel mech.eng.

    Please help for the final design.
    Now I have Al6061 tube. I put some holes and attached some sst equipments on it by ordinary AL rivets.
    If alodine or similar is the best way for corrosion resistance against sea water I am going to coat entire mast with this.
    Please share your comments.
    Thanks
     
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